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 A217575 Numbers n such that floor(sqrt(n)) = floor(n/floor(sqrt(n)))-1. 5
 2, 6, 7, 12, 13, 14, 20, 21, 22, 23, 30, 31, 32, 33, 34, 42, 43, 44, 45, 46, 47, 56, 57, 58, 59, 60, 61, 62, 72, 73, 74, 75, 76, 77, 78, 79, 90, 91, 92, 93, 94, 95, 96, 97, 98, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 132, 133, 134, 135, 136 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS One of four sequences given by classifying natural numbers according to the value of floor(sqrt(n)). See the paper in Link lines and A005563, A217570, A217571. Can be interpreted as a triangle read by rows: T(n,k) = n*(n+1)+k-1 with n>0, k=1..n. - Bruno Berselli, Oct 11 2012 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 Takumi Sato, Classification of Natural Numbers FORMULA a(n) = A063657(n) - 1. - Reinhard Zumkeller, Jun 20 2015 EXAMPLE As a triangle (see the second comment) this begins: 2; 6, 7; 12, 13, 14; 20, 21, 22, 23; 30, 31, 32, 33, 34; 42, 43, 44, 45, 46, 47; 56, 57, 58, 59, 60, 61, 62; 72, 73, 74, 75, 76, 77, 78, 79; 90, 91, 92, 93, 94, 95, 96, 97, 98; etc. - Bruno Berselli, Oct 11 2012 MATHEMATICA Select[Range[200], Floor[Sqrt[#]]==Floor[#/Floor[Sqrt[#]]]-1&] (* Harvey P. Dale, Oct 06 2018 *) PROG (Visual Basic in Excel) Sub A217575() Dim x As Long, n As Long, y As Long, i As Long x = InputBox("Count to") For n = 2 To x y = Int(Sqr(n)) If y = Int(n / y) - 1 Then i = i + 1 Cells(i, 1) = n End If Next n End Sub (MAGMA) [n: n in [1..150] | Isqrt(n) eq Floor(n/Isqrt(n))-1]; // Bruno Berselli, Oct 08 2012 (PARI) is_A217575(n)=n\(n=sqrtint(n))-1==n  \\ - M. F. Hasler, Oct 09 2012 (Haskell) a217575 = subtract 1 . a063657  -- Reinhard Zumkeller, Jun 20 2015 CROSSREFS Cf. A005563, A217570, A217571. Cf. A063657. Sequence in context: A226814 A233419 A189327 * A172154 A293531 A072147 Adjacent sequences:  A217572 A217573 A217574 * A217576 A217577 A217578 KEYWORD nonn AUTHOR Takumi Sato, Oct 07 2012 STATUS approved

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Last modified May 26 18:08 EDT 2020. Contains 334630 sequences. (Running on oeis4.)